1. Field of the Invention
The present invention relates to a lubricating device which discharges lubricating oil to a spindle apparatus provided in various high-speed rotary machines such as a machine tool and, especially, to the bearing of the spindle.
2. Description of the Related Art
Conventionally, in lubricating the bearing of a high-speed rotary spindle, normally, there are used lubricating devices of various types such as an oil mist type, an oil-air type, and a jet type.
The lubricating device of an oil mist type comprises an oil tank, a pump, a plunger, a pressure divider, compressed air, an electromagnetic valve, and a nozzle; and, in this device, lubricating oil is turned into a fine mist-like form, it is delivered through an air pipe using the compressed air, and it is jetted out to the interior portion of the bearing.
The lubricating device of an oil-air type comprises an oil tank, a pump, a distributor, a compressed air source, a plunger, and a nozzle; and, in this device, lubricating oil drops (0.01–0.03 ml) adjusted to a given quantity by the mechanical mechanism of the plunger is discharged into an air pipe, is delivered up to the nozzle by the compressed air, and is jetted out to the interior portion of the bearing.
The lubricating device of a jet type is a device which does not use the air source but turns lubricating oil into high pressure one using a high-pressure pump and jets out the high-pressure lubricating oil at a high speed into the interior portion of the bearing from a nozzle of which discharge diameter is narrowed.
By the way, while a current trend requests an increase in the rotation speed of the spindle device, in the lubricating devices of various types used for lubrication of the spindle device, there are found the following problems:
Firstly, in the lubricating device of an oil mist type, due to use of the compressed air, not only there arises a noise problem but also the mist-like lubricating oil scatters into the air to worsen an operation environment. Also, because of the scattering of the mist-like lubricating oil into the air, the quantity of lubricating oil to be supplied to the interior portion of the bearing is indefinite. Especially, in case where the bearing is rotated at a high speed, due to the effect of an air curtain, when dm·N is equal to or larger than 2000000 (dm expresses the pitch circle diameter of the bearing (mm), and N expresses the rotation speed (min−1) of the bearing), the lubricating oil can be little supplied to the interior portion of the bearing, thereby raising a fear that the bearing can cause seizure.
In the lubricating device of an oil-air type, similarly to the above-mentioned oil mist type lubricating device, since the compressed air is used, not only there arises a noise problem but also the mist-like lubricating oil scatters into the air to thereby worsen the operation environment. Also, in the high-speed rotation of the bearing, as the result of the rotation of the spindle, there is produced an air curtain. Therefore, similarly, the lubricating oil can be little supplied to the interior portion of the bearing, thereby raising a fear that the bearing can cause seizure.
Also, in the lubricating device of an oil-air type, because it is difficult to supply a fine amount of lubricating oil continuously and stably, the lubricating oil must be supplied intermittently and thus the lubricating oil is supplied at a given quantity (normally, in the range of 0.01–0.03 ml) every given interval time (normally, in the rage of 8–16 min.) into the air pipe. Therefore, since the quantity of lubricating oil to be supplied to the interior portion of the bearing varies every given time, the lubricating condition of the interior portion of the bearing varies all the time and, especially, just after the lubricating oil is supplied, a large quantity of lubricating oil enters the interior portion of the bearing, thereby causing a phenomenon that the torque of the bearing and the temperature of the bearing can vary. There is a fear that this phenomenon can have ill effects on the working precision of a machine tool.
On the other hand, in a lubricating device of a jet type, when compared with the above lubricating devices of oil mist and oil-air types, there is little found the effect of the above-mentioned air curtain but, not only because there is required an attendant device such as a high-pressure pump but also because the quantity of lubricating oil to be supplied to the bearing increases to thereby increase drag resistance, there is necessary a large motor which is used to drive the spindle, which results in the increased cost.
As a device which has solved the difficulty in the above-mentioned fine quantity adjustment of a lubricant, there are known devices which are respectively disclosed in the following patent publications.
That is, in Japanese Patent Examined Publication No. 2-15003 of Heisei, there is disclosed a device for supplying a fine fixed quantity of liquid. In this supply device, a piezo-electric element is used to allow the fine quantity adjustment of the liquid and a lubricant is delivered to a nozzle by compressed air.
In a flow control valve disclosed in Japanese Patent Examined Publication No. 7-65695, a diaphragm is disposed in one end of a magnetostrictive element and an orifice is adjusted by the expansion and contraction of the magnetostrictive element to thereby adjust the flow quantity and pressure of fluid.
In a giant magnetostrictive material pump disclosed in Japanese Patent Unexamined Publication No. 3-222877 of Heisei, the displacement of a giant magnetostrictive material is enlarged by a lever, and a diaphragm is driven by the lever to turn the pressure of the interior portion of the pump into a negative pressure or a positive pressure, thereby sucking or discharging a fluid.
In a magnetic precision pump (Magnetostrictive Pump) disclosed in U.S. Pat. Nos. 4,795,318 and 4,804,314, in the interior portion of a cylinder, there is disposed a piston which is formed of a magnetostrictive material and a voltage is applied to a coil, which is disposed in such a manner that it encloses the piston, to thereby expand and contract the piston so as to discharge a fluid in the interior portion of the cylinder.
In a giant magnetostrictive material type injection pump disclosed in Japanese Patent Unexamined Publication No. 4-81565 of Heisei, a needle valve is opened and closed by a giant magnetostrictive material to thereby inject a fixed quantity of high-pressure liquid.
However, in the above-mentioned pump using a giant magnetostrictive material or flow control valve, there are found the following problems.
The fine fixed quantity liquid supply device disclosed in Japanese Patent Examined Publication No. 2-15003 of Heisei has not solved yet a drawback caused by delivering the lubricant to the nozzle using the high-pressure air.
In the flow control valve disclosed in Japanese Patent Examined Publication No. 7-65695, the diaphragm area, to which the pressure of the liquid is applied, is larger than the sectional area of the giant magnetostrictive material and the liquid pressure is smaller than the pressure of the giant magnetostrictive material.
In the giant magnetostrictive material pump disclosed in Japanese Patent Unexamined Publication No. 3-222877 of Heisei, since the displacement is enlarged by the lever, the liquid pressure is smaller than the pressure of the giant magnetostrictive material. The output of the giant magnetostrictive material increases as a magnetic field by a coil is increased. However, in case where the coil magnetic field is increased, the required volume of the coil increases accordingly. As a result of this, a device using such coil increases in size.
In the magnetic precision pump disclosed in U.S. Pat. Nos. 4,795,318 and 4,804,314, since the piston itself is made of a drive element, the pressure of the lubricant cannot be made larger than the pressure of the giant magnetostrictive material.
The giant magnetostrictive material type injection pump disclosed in Japanese Patent Unexamined Publication No. 4-81565 of Heisei does not have a function to turn the pressure of the liquid into high pressure.
Further, in the oil-air lubricating method, there is used a fixed-quantity valve which is capable of mixing lubricating oil of the order of 0.01–0.03 ml per shot with air at given time intervals. As an example of the fixed-quantity valve, for example, there is known a valve which is disclosed in JP-B-8-2578U. This type of fixed-quantity valve is conventionally structured such that a fixed quantity of lubricating oil can be stored therein and can be discharged therefrom by making use of the reciprocating motion of a piston; specifically, the lubricating oil is stored in a cylinder disposed on one side of the piston and the lubricating oil is discharged on the opposite side of the piston. To reduce the oil discharge quantity, there can be expected a technique of reducing the diameter and stroke of the piston. However, in the conventional oil-air lubricating method, there are dimensional limits, for example, the sizes of sealing parts such as an O-ring and the size of a return spring, which makes it difficult to reduce the diameter and stroke of the piston. For this reason, it has been believed difficult to discharge a quantity of less than 0.01 ml of lubricating oil.
In addition, since the conventional lubricating apparatus employing the above-mentioned oil-air lubricating method is structured such that a given quantity of lubricating oil is stored therein and is discharged therefrom by use of the reciprocating motion of a single piston, a supply oil quantity per shot is normally large, that is, of the order of 0.03 ml and the lubricating oil is discharged at time intervals of approx. 15 min., thereby raising a problem that the temperature of the constantly rotating bearing can pulsate at the oil shot intervals. Also, in some cases, there are generated whizzing sounds between the rolling bodies and the mixed oil-air. The whizzing sounds between the rolling bodies and the mixed oil-air, when their frequencies are in the range of 2–3 KHz or less, in most cases, provide harsh noises. This raises a problem even in the case of a spindle which does not rotate at a very high speed, that is, when the product (dm·N) of the shaft diameter [mm] and the shaft rotation speed [min−1] is 1500000 or less.
On the other hand, regarding a pipe structure for supply of a fine quantity of lubricating oil, FIG. 84 shows a lubricating apparatus of an oil-air type using an air flow as a medium. As the state of connection of the end faces of two housings is shown in FIG. 85A, a pipe passage 902 serving as an oil flow passage formed in a housing is sealed by O-rings 904 which are disposed on the housing end faces. Also, as the state of connection between the nozzle frame 906 and pipe passage 902 is shown in FIG. 85B, oil-air is supplied to the nozzle frame 106 through the pipe passage 902. However, in the case of a fine quantity of lubricating oil being supplied, in a pipe arrangement structure using such O-rings 104, when the lubricating oil is jetted out, the volume of the interior portion of the pipe passage is caused to vary due to the elastic deformation of the O-rings 904, which makes it impossible to supply a given quantity of lubricating oil.